Most structural data of membrane peptides are deduced from experiments made at very low temperature where most dynamic processes are frozen. Unfortunately, at physiological temperature 13C-NMR intensities of peptides are attenuated relative to the predicted values given by the peptide:lipid molar ratio, resulting in a poor signal to noise ratio. This phenomenon had been attributed to a motional interference between the coherent motion of 1H decoupling (or MAS) with the incoherent dynamics of the peptide in the lipid bilayer. The signal losses are most pronounced when the rate of motion is close to the decoupling field strength (or spinning speed for the case of MAS). The types of motions that are thought to give rise to the aforementioned interference include: slow axial diffusion and/or a wobbling of the lipid long axis. To test some of these hypothesis we have synthesized and purified specifically 13C and 13C,2H labeled Gramicidin A (GA), whose structure in lipid bilayers is well known, and reconstituted the labeled peptides into DMPC bilayers. Preliminary results comparing 13C intensity in both 1H decoupled and undecoupled spectra of 13CH3 Alanine in GA in DMPC (Ala-GA/DMPC) indicate signal losses of at least a factor of two relative to 13CD3 labeled Ala-GA/DMPC. These results support the notion that there is interference between the motion of GA and the 1H decoupling field. Identification of the source of signal loss in the NMR of membrane peptides at physiological temperatures suggest that a general strategy for obtaining high resolution 13C spectra of such systems would include selective 2H labeling of amino acids of interest. The recovery of full 13C resonance intensities will allow the evaluation of whether or not homonuclear dipolar recoupling schemes could be employed to determine the structure of membrane peptides under physiological conditions.